A pump jack is a surface drive mechanism for a reciprocating piston pump in an oil well, and is used to mechanically lift oil or other liquids out of the well when there is insufficient subsurface pressure. Pump jacks are typically used onshore in relatively oil-rich areas. Modern pump jacks typically are powered by a electric motor, and the pump jack converts the motive force of the motor to a vertical reciprocating motion to drive the pump shaft (thereby causing a characteristic nodding motion). Electrical power usually is obtained from the electrical grid of the local electric utility or power supplier.